The present invention relates to a process of hydrogenating a nitrile-diene copolymer rubber.
Nitrile rubbers obtained by the emulsion copolymerization of (meth)acrylonitrile with conjugated dienes, for example, butadiene, and optionally small amounts of other comonomers are known, for example, from German Pat. No. 658,172. In addition, it is known from U.S. Pat. No. 3,700,637 that nitrile rubbers of this type can be hydrogenated, the strength of the products thus obtained being improved, compared with the non-hydrogenated starting material.
According to German published Patent Application No. 25 39 132, the hydrogenation of statistical acrylonitrile butadiene copolymers in solution also gives products having improved properties. In this case, the reaction is selective with respect to the extent of hydrogenation.
It has now been found that metal-complex catalyzed hydrogenation of a nitrile-diene copolymer rubber, in the presence of a cocatalyst, can be accelerated by the addition of a small amount of a proton acceptor that is non-coordinating with the metal-complex catalyst. In addition, it has also been found that the amount of co-catalyst used can be lowered in the presence of the proton acceptor.
Accordingly, the present invention provides a process of hydrogenating a nitrile copolymer rubber, which comprises subjecting the copolymer to hydrogenation in the presence of a hydrogenation catalyst, a co-catalyst, and a proton acceptor that is non-coordinating with the metal-complex catalyst.